Flight miles are measured in nautical miles in the vast majority of the world's airspace. Kindly don't pander to those ignorant of anything but the metric system when writing articles such as this. To do so when referring to flight in the USA is especially ludicrous.

As a non-pilot and non-sailor, I have no idea how long a nautical mile is (although I do know it is longer than a regular mile). Since the Economist is printed for the general public, it ought to express distance in units the general public understands. Besides, 7 - 0.3 billion people understand SI. Only 0.3 billion use the abomination that is the imperial system.

You are aware, I trust, that by law the metric system is the legal standard in the US. Miles, gallons, etc. are all legally defined in terms of their metric equivalents -- have been for over a century. And Federal government agencies have, for decades, been under a legal requirement to use metric measures.

One's safest air travel experience will always be found by stepping onto a scheduled airliner which does the same route every single day, being flown by a pilot/s who does the same route in that same aircraft every single day, backed up and guided by the same air traffic controllers who track that same aircraft, and pilot, every single day, as well as the same mechanics who maintain that same aircraft every single day. The continuous and cumulative learning curve travel of these participants has the effect of steadily reducing risk. Similarly, the enormous economic stakes for commercial aircraft companies to deliver aircraft which have the safest possible records, also contributes to air safety.

Traveling via private aircraft, including corporate jets, and self-piloted aircraft of any type, cannot ever come close to the above risk-reducing effects, and as such, account for an enormous percentage of aircraft accidents, mishaps and deaths.

One of the most effective ways to shorten one's expected lifespan is to purchase and pilot one's own private aircraft -- or get into a private aircraft piloted by another.

Eventually efforts at improved safety reach a point of diminishing returns for any risk. Perhaps a measure of safety might be how much more money has to be invested in a risk to reduce the equivalent number of deaths.

My approach would not require assigning a definite value, but assessing costs and setting priorities by comparing costs. In software engineering a developer is always faced with a long list of bugs. He generates a pareto chart and works on those that are the most important. Eventually, he gives up and moves on to another activity where there are more important problems. In contrast, social engineers do not set priorities, except, perhaps using subjective criteria.

Is it more important to focus on fixing problems with African airlines or creating jumbo jets that can land on water, as somebody suggested? And are airplane crashes in Africa more important than reducing malaria deaths?

I can pass on a story that may explain part of why corporate jets have a worse safety record than commercial. The pilot-in-command is so in fact, and can refuse to fly for any of a number of reasons, at his sole discretion, but weather along the route is the most common. The retired pilot I was talking to had over 30,000 hours of corporate flight time - an expert by any standard. He told me of a CEO in Florida with his family, who WAS going to fly back to New York NOW. But there were icing conditions on the way, and my pilot friend refused to go. Of course, he was fired on the spot, but finding another pilot immediately was impossible. Shortly thereafter, when her husband was out of earshot, the CEO's wife thanked the pilot profusely for refusing to put her, her children, and even her foolish husband at risk of their lives.
Which begs the question. How many corporate pilots swallow their better judgement to appease the boss?

IIRC from my graduate risk analysis course, most airline accidents happen during takeoff and landing, so one of the more apropos comparisons is between the safety of air travel and a given number of miles driven on a certain type of road. For example, the distance one might travel on an interstate highway to equal the level of risk of an accident from an airplane ride will be much larger than if one were driving on a country road or city street.

Considering that almost all air accidents occur on the ground (including after falling out of the sky), perhaps the comparison should be made of miles travelled when actually on the ground. Air travel might not look so attractive then.

That's preposterous. Such a comparison would only make sense if and only if the main mode of travel were on the ground, and again the record would be vastly different because the accident occur not while the plane is taxi-ing but while it is transitioning from the ground to the air or vice-versa.